(12) United States Patent 

Zecha et ai. 

(54) SHEAR THINNING VINYL ACETATE BASED 

POLYMER LATEX COMPOSITION, 

ESPECIALLY FOR ADHESIVES 

(75) Inventors: Helmut Zecha, Burghausen (DE); 

Rudolf Weissgerber, Burghausen (DE); 

Francis Petrocelli, Allentown, PA (US) 

(73) Assignee: Air Products Polymers, L.P., 

Allentown, PA (US) 

( *) Notice: Subject to any disclaimer, the term of this 

patent is extended or adjusted under 35 

U.S.c. 154(b) by 361 days. 

(21) Appl. No.: 10/035,373 

(22) 

(65) 

(51) 

(52) 

(58) 

(56) 

DE 

EP 

EP 

EP 

EP 

EP 

EP 

EP 

EP 

JP 

JP 

WO 

Filed: Oct. 19, 2001 

Prior Publication Data 

US 2003/0109620 A1 Jun. 12, 2003 

Int. CI? . ... ..... ... ... ... ..... ... .... C08F 2/38; C08J 3/00; 

C08K 5/05; C08K 3/20; C08L 11/02 

U.S. CI. ......................... 526/85; 524/379; 524/387; 

524/388; 524/457; 524/459; 524/503; 524/524; 

524/556; 524/557; 524/563; 526/82 

Field of Search ................................. 524/379, 387, 

524/388, 457, 459, 503, 524, 556, 557, 

563; 526/85, 82 

References Cited 

U.S. PATENT DOCUMENTS 

4,128,518 A 

5,391,608 A 

5,434,216 A 

5,439,960 A 

* 12/1978 Oyamada et al. ........... 524/501 

2/1995 Mudge et al. .............. 524/459 

7/1995 Mudge et al. .............. 524/803 

8/1995 Mudge et al. .. ... ... ... ... 524/111 

FOREIGN PATENT DOCUMENTS 

2620738 

0322175 

0433957 

0501174 

0561221 

0623661 

0686683 

0812863 

1170311 

6322337 

9302004 

01/00695 

12/1977 

6/1989 

6/1991 

9/1992 

9/1993 

11/1994 

12/1995 

12/1997 

1/2002 

11/1994 

11/1997 

1/2001 

OlliER PUBLICATIONS 

G. E. Ham, et aI., Vinyl Polymerization, 1967, vol. I, Chap. 

4, pp. 207-329. 

M. K. Lindemann, The Mechanism of Vinyl Acetate Polymerization. 

111111 1111111111111111111111111111111111111111111111111111111111111 

US006794466B2 

(10) Patent No.: 

(45) Date of Patent: 

US 6,794,466 B2 

Sep.21,2004 

H. Y. Erbil, Vinyl Acetate Emulsion Polymerization and 

Copolymerization with Acrylic Monomers, CRC Press 2000. 

J. Brandrup, et aI., Polymer Handbook, John Wiley Sons, 

Inc., 4th Ed., 1999, P 11/97 ff. 

* cited by examiner 

Primary Examiner-Patrick D. Niland 

(74) Attorney, Agent, or Firm-Mary E. Bongiorno 

(57) ABSTRACT 

The present invention elates to a vinyl acetate based polymer 

latex composition obtained by emulsion polymerization of: 

(a) polyvinyl alcohol, 

(c) a monomer mixture comprising vinyl acetate, and (d) 

optionally one or more additional co-monomer(s), 

in presence of (c) 0.0001-0.05 wt. % of a chain transfer 

agent, based on total monomer weight, said vinyl acetate 

based polymer latex composition having a weight average 

particle size ~400 nm and a higher shear thinning factor 

than the vinyl acetate based polymer latex composition (a), 

(b) and (d) obtained in the absence of the chain transfer 

agent (c). According to one embodiment, emulsion polymerization is carried out in presence of 0.001 to 0.05 wt. % 

of a chain transfer agent selected from the group consisting 

of aldehydes and chain transfer agents having a similar chain 

transfer constant with regard to vinyl acetate as the monomer. According to another embodiment, emulsion polymerization is carried out in presence of 0.0001 to 0.01 wt. % of 

a chain transfer agent selected from the group consisting of 

thiols, mercapto acids, and chain transfer agents having a 

similar chain transfer constant with regard to vinyl acetate as 

the monomer. The invention also relates to an adhesive 

comprising said vinyl acetate based polymer latex composition. Such adhesive is preferably used in paper and packaging applications or as a wood working adhesive or wood 

glue. 

The invention further relates to a process of manufacture of 

a vinyl acetate based polymer latex composition having a 

weight average particle size >400 nm, including emulsion 

polymerization of vinyl acetate in the presence of polyvinyl 

alcohol, optionally together with one or more additional 

co-monomer(s), wherein the emulsion polymerization is 

carried out in the presence of 0.0001 wt. % to 0.05 wt. % 

chain transfer agent, based on total monomer weight. 

25 Claims, No Drawings 
US 6,794,466 B2 

1 

SHEAR THINNING VINYL ACETATE BASED 

POLYMER LATEX COMPOSITION, 

ESPECIALLY FOR ADHESIVES 

BACKGROUND OF THE INVENTION 

2 

adhesive obtained, especially its rheological properties such 

as viscosity and shear thinning, or the setting speed. Rheology mainly depends on the molecular weight distribution 

and degree of hydrolysis of the polyvinyl alcohol used, but 

5 can be changed by altering product recipe. For example, 

EP-A-0,686,683 discloses altering the rheological properties 

by altering the formulation with some thickening agent, 

thereby changing the continuous phase viscosity, at the Polymer emulsions or polymer latices prepared by conventional emulsion homo- or co-polymerization of vinyl 

acetate using polyvinyl alcohol as protective colloid are 10 

widely used for adhesives. There are several application 

fields for such emulsions such as in wood glues, paper and 

packaging adhesives (e.g. case sealing, book binding, bag 

making, card board lamination), parquet adhesives and 

others. Most importantly these latices are used in paper and 

packaging or in woodworking adhesive formulations or 

wood glues. 

expense of an altered recipe. 

EP 00 114097.9, assigned to Air Products Polymers LP, 

discloses adjustment of rheological properties and expecially reduction of shear thinning of a latex emulsion by 

increasing particle size of the polymer without changing 

overall composition. More in detail, the document teaches 

15 increasing particle size by carrying out emulsion polymerization of vinyl acetate and optional co-monomers in presence of a pre-crosslinking monomer selected from ethylenically unsaturated monomers such as triallyl cyanurate and 

allyl methacrylate. The document is silent on the possibility 

All these adhesives and especially woodworking adhesives are optimized with respect to several properties such as 

water resistance of the bond, heat resistance of the bond and 

creep of the bond. Further, before application several dispersion properties must be met. These are compatibility with 

formulation aids such as film forming agents, fillers, metal 

salts; rheological properties; storage stability; the setting 

speed and so on. 

20 of increasing shear thinning factor. 

With the term shear thinning the phenomenon of a viscosity drop with increased shear rate is addressed. Such 

decrease of viscosity is considered reversible if viscosity 

reaches the original value when the shear rate is decreased 

25 to its original value. 

Vinyl acetate (VAc) based polymer latices for paper and 

packaging have to meet certain requirements regarding 

setting speed, penetration into the paper, open time, cohesion of the bond. On the other hand they should possess good 

re-dispersability of a film to provide good machine cleaning 30 

properties. 

Shear thinning can be quantified by the so called "shear 

thinning factor" (SF) which is obtained as the ratio of 

viscosity measured by Brookfield viscosimeter at 1 rpm, 

Bf(l), and at 10 rpm, Bf(lO): 

SF ~((Bfl/Bf1 0)-1). 

A shear thinning factor below zero (SF<O) indicates shear 

thickening, a shear thinning factor of zero (SF=O) indicates 

Newtonian behavior and a shear thinning factor above zero 

35 (SF>O) stands for shear thinning behavior. Shear thinning 

factors;'O reflect properties of emulsions with high solids 

content as is typically the case for VAc based latices. 

Non-Newtonian behavior is in general no problem at lower 

VAc based polymer latices for woodworking adhesives 

having good water resistance typically use some functional 

post-crosslinking co-monomer in polymerization and the 

formulation with a catalyst afer polymerization. Amongst 

the post-crosslinkers N-alkylol derivatives of an amide of an 

a,~-ethylenically unsaturated carboxylic acid, such as 

N-methylol acrylamide (NMA) which is preferred for latex 

wood glues are known. For example, U.S. Pat. No. 5,439, 

960 and U.S. Pat. No. 5,391,608 describe the use of 0.1 to 40 

6% of NMA based on total monomer content Likewise 

European Patent Application EP-A-0,561,221 describes the 

use of 2 to 10% NMA. 

solids contents (e.g. below 40%). 

It is an object of the present invention to find a possibility 

for independent control of the shear thinning factor which in 

turn allows to precisely and intentionally adapt the emulsion 

or latex for certain applications thereby improving performance of for example a paper and packaging adhesive or of As the catalyst for formulation of the above woodworking 

adhesives having good water resistance water-soluble metal 

salts of monobasic acids such as aluminumm(III), chromium 

and/or zirconium(IV) salts, especially aluminum nitrate, 

chromium chloride or zirconium oxychloride are used (see 

for example DE-26,20,738, EP-A-0,433,957, EP-A-0,501, 

174, EP-A-0,686,683 and U.S. Pat. No. 5,434,216). 

Another approach to improve water resistance of wood 

glues is for example disclosed in EP-A-0,433,957, EP-A-O, 

623,661 and lP-06,322,337 which documents relate to use 

of more hydrophobic co-monomers such as vinyl pivalate, 

diisopropyl maleate, diisopropyl fumarate, vinyl chloride or 

versatic acid vinyl esters for this purpose. 

Adhesive performance of for example a wood glue is 

typically controlled by the amount of polyvinyl alcohol, i.e. 

the ratio of polyvinyl alcohol to monomer, the polyvinyl 

alcohol molecular weight and its degree of hydrolysis as for 

example disclosed in U.S. Pat. No. 5,434,216. In addition, 

functionalized polyvinyl alcohols, e.g. acetoacetylated polyvinyl alcohols or itaconic acid-modified polyvinyl alcohols, 

or ethylene modified PVOH may be used. 

The choice of the polyvinyl alcohol (PVOH) determines 

other properties of the vinyl acetate latex and thus the 

45 a woodworking adhesive or wood glue. 

In several cases it would be especially useful and desirable to control shear thinning i.e. the shear thinning factor 

and to provide the desired extend of it. More specifically, it 

would in the first place be desirable to avoid any shear 

50 thickening i.e. to be in the position to shift the shear thinning 

factor from negative to positive values (SF>O). Performance 

requirements for a paper and packaging adhesive are, 

however, typically a SF within the range of O.l<SF~l.5 

dependent on the specific application, whereas performance 

55 requirements for a wood glue are typically a SF in the range 

of 0.1<SF~0.6. In any case shear thickening (SF<O) is 

preferably to be avoided. 

Additionally, the requirements for setting speed and cohesion must be fulfilled: In the case of a paper and packaging 

60 adhesive setting speed measured as AZG in seconds should 

be:<4 s, whereas cohesion measured at 70° C. should be~4 

N/mm2. 

In the case of a woodworking adhesive (wood glue) the 

setting speed measured as bond strength after 2.5 minutes 

65 gluing time should be>l.5 N/mm2. Cohesion of the wood 

bond measured as bond strength at 80° C. should be>6 

N/mm2. 
US 6,794,466 B2 

3 4 

together with one or more additional co-monomer(s), 

wherein the emulsion polymerization is carried out in the 

presence of 0.0001 to 0.05 wt. % of a chain transfer agent, 

based on total monomer weight. Preferably the chain transOther useful adhesive performance parameters created 

e.g. by the level of co-monomer such as NMA, and/or by the 

amount of PVOH and/or by its molecular weight and 

hydrolysis distribution, should remain more or less 

unchanged. 5 fer agents and the amounts used are as defined above. 

It is thus another object of the invention to provide a wood 

glue which meets the above requirements and has improved 

water resistance. 

According to a third aspect the present invention relates to 

an adhesive, comprising the vinyl acetate based polymer 

latex composition as defined above. 

BRIEF SUMMARY OF THE INVENTION 

The above objects are solved and the drawbacks of the 

prior art are overcome according to a first aspect of the 

invention by a vinyl acetate based polymer latex composition obtained by emulsion polymerization of: 

According to a preferred embodiment the adhesive is for 

10 use as a fast setting adhesive for paper and packaging, said 

adhesive comprising a vinyl acetate homopolymer latex 

composition. 

According to another preferred embodiment the adhesive 

is for use as a wood glue and comprises a vinyl acetate based 

(a) polyvinyl alcohol, 

(b) a monomer mixture comprising vinyl acetate, and 

optionally (d) one or more additional co-monomer(s), 

15 polymer latex composition of a copolymer of vinyl acetate/ 

N-methylol acrylamide, optionally further including versatic 

acid vinyl ester having 9 to 13 carbon atoms from the 

carbonic acid group. The chain transfer agent is preferably 

mercapto propionic acid. 

in presence of (c) 0.0001 to 0.05 wt. % (1 to 500 ppm) of a 

chain transfer agent (CTA), based on total monomer weight, 

said vinyl acetate based polymer latex composition having a 20 

weight average particle size~400 nm and a higher shear 

thinning factor than the vinyl acetate based polymer latex 

composition obtained in the absence of the chain transfer 

agent. 

According to a first embodiment the emulsion polymer- 25 

ization is carried out in presence of 0.001 to 0.05 wt. % of 

a chain transfer agent selected from aldehydes, especially 

C2 _

s-aldehydes and other CTAs having a similar chain 

transfer constant with regard to VAc as the monomer. 

According to a second embodiment the emulsion poly- 30 

merization is carried out in presence of 0.0001 to 0.01 wt. % 

DETAILED DESCRIPTION OF THE 

INVENTION 

The present invention is based on the surprising finding 

that the shear thinning factor of a vinyl acetate based 

polymer latex prepared by conventional emulsion polymerization using PVOH as a protective colloid can be increased 

without substantially changing the latex composition, especially without changing the type and/or amount of PVOH. 

This can be achieved by polymerizing the vinyl acetate in 

presence of a small amount of a chain transfer agent without 

a significant change of the average molecular weight, measured as the K-value. Thereby other important adhesive 

properties, such as cohesion, remain unchanged, whereas the 

shear thinning may be adjusted as desired and/or a shear 

of a chain transfer agent selected from thiols, especially 

C2 _

s-thiols, mercapto acids, especially C2 _S-mercapto acids 

and other CTAs having a similar chain transfer constant with 

regard to VAc as the monomer. 35 thickening may be even reversed to shear thinning. 

The latex of the invention preferably has a shear thinning 

factor of about 1,2 to 3,5 times the shear thinning factor of 

a latex composition obtained in absence of the chain transfer 

agent or wherein the shear thinning factor is shifted from 

negative values to positive values as compared to the shear 40 

thinning factor of a latex composition obtained in absence of 

the chain transfer agent. 

Preferably, the latex weight average particle size is about 

60 to 95% the weight average particle size of a latex 

composition obtained in the absence of the chain transfer 45 

agent. 

Preferably, the chain transfer agent is selected from the 

group consisting of aldehydes, preferably C2 _s-aldehydes, 

thiols, preferably C2 _

s-thiols, mercapto acids, preferably 

C2 _

s-mercaptoacids, and mixtures thereof. More preferably 50 

the chain transfer agent is selected from the group consisting 

of acetaldehyde, croton aldehyde, propionic aldehyde, 

2-mercapto propionic acid, 3-mercapto propionic acid, and 

mixtures thereof. 

The amount of vinyl acetate is preferably in the range of 55 

100 wt. % to 60 wt. %, based on total monomer weight. 

According to an especially preferred embodiment the 

vinyl acetate based polymer latex composition is a copolymer of vinyl acetate/N-methylol acrylamide, optionally further including versa tic acid vinyl ester having 9 to 13 carbon 60 

atoms from the carbonic acid group. The chain transfer agent 

is then preferably a mercaptopropionic acid. 

According to a second aspect the present invention relates 

to a process of manufacture of a vinyl acetate based polymer 

latex composition having a weight average particle 65 

size~400 nm, including emulsion polymerization of vinyl 

acetate in the presence of polyvinyl alcohol, optionally 

More in detail, the invention to a first aspect thereof thus 

relates to a vinyl acetate based polymer latex composition 

obtained by emulsion polymerization of: 

(a) polyvinyl alcohol, 

(b) a monomer mixture compnsmg vinyl acetate, 

optionally (d) one or more co-monomer(s), 

and 

in presence of (c) 0.0001 to 0.05 wt. % (1 to 500 ppm) of a 

chain transfer agent, based on total monomer weight, said 

vinyl acetate based polymer latex composition having a 

weight average particle size ~400 nm. The resulting VAc 

based polymer latex composition has a higher shear thinning 

factor than the VAc based polymer latex of the same 

composition (a), (b) and optionally (d) which is obtained in 

absence of the chain transfer agent ( c). At the same time, the 

K-value indicating molecular weight is surprisingly slightly 

increased or remains about comparable. 

The use of a chain transfer agent (CTA) in emulsion 

polymerization of VAc monomers is well known in the art 

and is described in textbooks, e.g. "Vinyl Polymerization", 

edited by George E. Ham, Marcel Dekker, 1967, Vol. I, 

Chapter 4, pages 207-329: M. K. Lindemann, "The Mechanism of Vinyl Acetate Polymerization" or "Vinyl Acetate 

Emulsion Polymerization and Copolymerization with 

Acrylic Momnomers" by H. Y. Erbil, CRC Press 2000. 

The latter textbook teaches that CTAs can be included in 

emulsion polymerization to terminate propagating polymer 

chains and to prevent polymer chains from growing too 

large, which may create problems in subsequent applications. Changing the concentration of such modifiers or CTAs 

during emulsion polymerization leads to control of average 
US 6,794,466 B2 

5 

molecular weight, molecular weight distribution, branching, 

and crosslinking of the polymer. The extend of chain transfer 

can be predicted if the chain transfer constants Cx are known 

for a given monomer system. 

6 

Astonishingly, these effects can be obtained for both VAC 

homopolymers and VAC copolymers comprising additional 

co-monomers such as e.g. NMA, ethylene and/or versa tic 

acid esters. 

Chain transfer constants Cx may be obtained as explained 5 

e.g. in the "Polymer Handbook", edited by J. Brandrup, E. 

The chain transfer agent for use in the invention may be 

selected from the group consisting of aldehydes, preferably 

C2 -Cs-aldehydes, such as acetaldehyde, propionic 

aldehyde, butyraldehyde, croton aldehyde, and n-pentanal; 

thiols, preferably C2 -Cs-thiols such as ethanthiol, 

H. Immergut, and E. A. Grulike, John Wiley Sons, Inc., 4. 

Edition, 1999, page 11/97 ff. Various transfer constants of 

vinyl acetate to different species are given there. As known 

radical transfer of a growing polymer chain may occur to 

any species involved in the polymerization: monomer; polymer; protective colloid, such as PVOH; emulsifier, if used; 

initiator; solvent, if is used; or additives called chain transfer 

agents. Chain transfer constants of a certain species (Cx ), 

may be different by several orders of magnitude in different 

monomer systems. 

Examples of CTAs used in VAc based latices include, but 

are not limited to mercaptanes/thiols, aldehydes, chlorinated 

aliphatics and so on. The CTAs are usually characterized by 

their chain transfer constant. To effect chain transfer CTAs 

are typically used in appreciable amounts. For example EP 

0,332,175 discloses the use of chain transfer agents in 

emulsion polymerization of VAc based polymer latices. The 

specific chain transfer agents described in said document are 

used in an amount of 0.1 to 0.7 wt. %. The resulting polymer 

latices are disclosed to show an improved setting speed. 

WO 01100 695 discloses a method for radically initiated, 

aqueous emulsion polymerization for producing an aqueous 

polymer dispersion with polymer particles having a weight 

average particle diameter~ 300 nm. According to said 

method, at least one monomer with at least one ethylenically 

unsaturated group, preferably an acrylic monomer, is dispersed in an aqueous medium and polymerized using at least 

one radical polymerization initiator in the presence of at 

least one radical chain transfer agent «5 wt. %) with a 

solubility greater than 1xlO-s mol per kilogram water at 20° 

C. and at 1 bar (absolute). The resulting dispersions have a 

solids content of about 20-30 wt. % 

When CTAs were used in emulsion polymerization, as 

given above (EP-A-0,322,175; JP-A-9,302,004; WO-A-Oll 

00695; EP-A-0,812,863) it was accepted or it was even a 

goal (JP-A-9,302,004) that the molecular weight of the 

obtained polymer decreased. As is well known in the art, 

such drop of molecular weight has a negative impact on the 

cohesion of a bond prepared by such lower molecular weight 

polymer. Only in few cases, e.g. for pressure sensitive 

adhesives, the lower molecular weight may influence tack 

and adhesion in the desired direction and the resulting loss 

of cohesion is acceptable. 

It was surprising to find that, upon use of trace amounts 

10 propanthiol, mercaptoethanol, 2- or 3-mercaptopropanol, lor 2-n-butane-thiol, and n-pentanethiol; and mercaptoacids, 

preferably C2 _

s-mercaptoacids, such as 2- or 3-mercapto 

propionic acid, and 2- or 3-mercapto butyric acid and 

mixtures thereof, mercapto acids being preferred. More 

15 preferably the chain transfer agent used in the present 

invention is selected from the group consisting of 

acetaldehyde, propionic aldehyde, croton aldehyde, 2- and 

3-mercapto propionic acid, and mixtures thereof. Most preferably the chain transfer agent is a mercapto propionic acid 

20 (MPA). Mixtures of CTAs may be used, provided the 

respective CTAs do not negatively interfere with each other. 

The amount of CTA used according to the present invention is in general in the range of 0.0001 to 0.05 wt % (1 to 

500 ppm), based on total monomer content, preferably 0.001 

25 to 0.05 wt. % (10 to 500 ppm). According to one embodiment the emulsion polymerization is carried out in presence 

of 0.001 to 0.05 wt % (10 to 500 ppm), preferably 0.001 to 

0.02 wt. % and most preferably 0.001 to 0.01 wt. %, of a 

chain transfer agent selected from the group consisting of 

30 aldehydes and CTAs having a similar chain transfer constant 

with regard to VAc as the monomer. According to an 

alternate embodiment the emulsion polymerization is carried out in presence of 0.0001 to 0.01 wt % (1 to 100 ppm), 

preferably 0.0001 to 0.005 wt. %, and most preferably 0.001 

35 to 0.0025 wt. %, of a chain transfer agent selected from the 

group consisting of thiols, mercapto acids, and CTAs having 

a similar chain transfer constant with regard to VAc as the 

monomer. All percentages are based on total monomer 

content. With the term "similar" as used above a chain 

40 transfer constant is addressed which with regard to VAc 

under polymerization conditions is in the same order of 

magnitude and preferably only slightly differs from the one 

of an aldehyde, thiol and mercaptoacid, respectively. 

The resulting polymer latex has a weight average particle 

45 size of~400 nm. Preferably such particle size is in the range 

of 500 to 1500 nm, more preferably 650 to 1500 nm, most 

preferably 700 to 1200 nm. Solids content of the emulsion 

is preferably equal to or above 40 wt. %, more preferably in 

the range of 45 to 70 wt. %, most preferably in the range of 

50 50 to 65 wt. %. At these high solids contents shear thinning 

or thickening, which is of no concern for polymer latices 

containing less solids «40 wt. %), needs to be paid careful 

attention. The shear thinning factor can be carefully and 

of a CTA, smaller final particle sizes are obtained which 

cause more shear thinning or which may even change a shear 

thickening behavior to a shear thinning one. At the same 

time, and even more surprisingly it was found, that latices 

polymerized in the presence of traces of one or more CTAs 55 

showed a clear tendency to faster setting speed. 

independently adjusted by the method of the invention. 

The CTA may be added to the initial reactor charge, 

before polymerization is started by adding the initiator, or 

may be fed to the reactor during the course of the polymerization. Conventional emulsion polymerization may be used 

as e.g. described in EP 00 114097.9. 

For PVOH stabilized VAc based polymer latices, when 

used as adhesives, a too low molecular weight would 

decrease the cohesion of the bond. For these types of 

adhesives high cohesion is required, which should be also 60 

sufficiently high enough at higher temperatures, named then 

as heat resistance. CTAs are therefore generally considered 

disadvantageous in such compositions. 

The polymer latex of the invention comprises vinyl 

acetate as the base monomer. Vinyl acetate is used in an 

amount of 100 to 60.0% by weight, based on total monomer 

content. Preferably, the amount of vinyl acetate used is in the 

It has surprisingly and unexpectedly been discovered that range of 100 to 80% by weight. According to one embodithe introduction of trace amounts of a CTA did not decrease 

the molecular weight of the resulting polymer, characterized 

by the K-value, but that the opposite was observed. 

65 ment the VAc based polymer latex may be a VAc homopolymer latex. These VAc homopolymer latices can advantageously be used for paper and packaging applications. The 
US 6,794,466 B2 

7 8 

The above unsaturated carboxylic acid as the co-monomer 

is an ethylenically unsaturated acid and may be selected 

from the group consisting of acrylic acid, methacrylic acid, 

croton acid, itaconic acid, maleic acid, fulmaric acid, their 

VAc based latex compositlon may also be a co-polymer 

composition. In this case one or more co-monomers selected 

from the following may be copolymerized with VAc: one or 

more post-crosslinking monomer(s), one or more vinyl 

ester(s), one or more ethylenically unsaturated acid(s) or 

anhydride(s) thereof, one or more acrylic acid(s), ethylene 

and mixtures of the foregoing. 

5 anhydrides such as maleic acid anhydride, and mixtures 

thereof. If used, the amount of the ethylenically unsaturated 

carboxylic acid or their mixtures is 0.1 to 3.0% by weight, 

preferably 0.5 to 2.0% by weight, based on total monomer If e.g. designed for wood glues the vinyl acetate based 

polymer latex of the invention, preferably comprises a 

post-crosslinking monomer selected from the group consist- 10 

ing of N-alkyol derivatives of an amide of an a,~­

ethylenically unsaturated carboxylic acid and mixtures 

thereof. Preferably the post-crosslinking monomer is 

selected from the group consisting of N-Cl _3 -alkylol (meth) 

acrylamides, preferably N-methylol (meth)acrylamide, 

N-Cl _3 -alkylol melamides, preferably N-methylol 

melamide, N-Cl _3 -alkylol melamic acid and their esters, 

preferably N-methylol melamic acid, N-methylol melamic 

acid ester, N-C2 _

s-acylol amides of vinylaromatic acids, 

N-Cl _4 -alkoxymethyl (meth)acrylamide, and mixtures 

thereof. More preferably, the post-crosslinking monomer is 20 

N-methylol acrylamide (NMA). 

With the term "(meth)acryl. .. " as used herein both the 

respective acrylic acid derivatives and the methacrylic acid 

derivatives are referred to. Thus, "N-methylol (meth) 

acrylamide" refers to both N-methylol acrylamide and 

N-methylol methacrylamide. The above Cl _

3 or Cl _4 alkly 

residues include methyl, ethyl, n-propyl, i-propyl, n-, i-, and 

t-butyl residues and may be chosen independently from each 

other. 

The post-crosslinking monomer is preferably comprised 

in the vinyl acetate based polymer latex composition of the 

invention in an amount of 0.1 to 5.0% by weight based on 

the total monomer content The post-crosslinking monomer 

or mixtures of such monomers is known to be essential for 

sufficient water and heat resistance of the bond. Use of such 

post-crosslinking monomer or monomer mixtures is therefore preferred. It is, however, not necessary to achieve the 

effects of the invention. Therefore, although preferred, the 

post-crosslinking monomer is not an essential component of 

the claimed latex composition. 

The vinyl acetate based polymer latex composition of the 

invention may comprise the above one or more copolymerizable co-monomers in the following amounts: up to 40% by 

weight vinylic ester, up to 15% by weight acrylic monomer, 

up to 3% by weight unsaturated carboxylic acid, and up to 

30% by weight ethylene, all percentages being based on total 

monomer content, or mixtures thereof, provided the total 

amount of copolymerizable co-monomers does not exceed 

50% by weight. 

content. 

The vinyl acetate based polymer latex composition may 

further comprise up to 30% by weight ethylene, preferably 

1 to 20% by weight ethylene based on total monomer 

contents. In a preferred embodiment, the vinyl acetate based 

polymer latex composition, which may optionally comprise 

15 the above post-crosslinking monomer, comprises one or 

both of 1 to 20% by weight ethylene and 1 to 30% by weight 

vinyl ester as the copolymerizable co-monomers, provided 

the total amount of copolymerizable co-monomer does not 

exceed 1 to 40% by weight. 

The colloidal stabilizer used in the vinyl acetate based 

polymer latex compositions of the invention is polyvinyl 

alcohol (PVOH). Various suitable polyvinyl alcohols are 

known to the skilled worker and are readily available. 

Especially preferred is a partially hydrolyzed PVOH having 

25 a degree of hydrolysis from 60 to 99 mol %, preferably from 

80 to 97 mol %, most preferably 86 to 94 mol %. To achieve 

the desired viscosity level of the polymer latex and to allow 

for good adhesion performance of the bond, blends of 

different PVOH grades possessing different molecular 

30 weights and hydrolysis distributions may be used. The 

colloidal stabilizer PVOH is typically used in an amount of 

3 to 15% by weight, based on the total weight of the 

composition, more preferably 4 to 11 % by weight. 

As put forth above, the PVOH is typically chosen to 

35 provide desired performance of the latex and/or the adhesive 

comprising the same, respectively. Rheological properties of 

the latex/adhesive likewise depend in part on the choice of 

the PVOH, but can be controlled independently by the use 

of CTAs according to the invention. This use of trace 

40 amounts of CTAs according to the invention results in 

reduced shear thickening, in trans ferring a shear thickening 

into a shear thinning one, or in more shear thinning i.e. in an 

increased of the shear thinning factor SF. Such change of 

rheological properties of vinyl acetate based polymer lattices 

45 using PVOH as the protective colloid, however, seemed to 

be impossible without changing the amount or the molecular 

properties of the PVOH The polymer latex particles may be 

co-stabilized by use of emulsifiers, if needed. These emulsifiers are known to the skilled worker and can be included 

Vinyl esters other than VAc which may be used in 50 

combination with vinyl acetate are for example vinyl 

propionate, vinyl pivalate, vinyl laurate, vinyl 2-ethyl 

hexanoate, dibutyl maleate, dioctyl maleate, diisopropyl 

maleate, diisopropyl fumarate, versa tic acid vinyl esters 

having 9 to 13 carbon atoms from the carbonic acid group, 55 

preferably 9 or 10 carbon atoms, or mieeuees thereof The 

amount of other vinyl esters, if used, is in the range of up to 

40.0% by weight, based on total monomer content, preferably 3 to 30% by weight. 

as usual. Preferably, non-ionic emulsifiers such as polyoxyethylene ethers or fatty alcohols may be used, preferably in 

an amount of 0.1 to 1.0% by weight, based on total monomer 

content. 

In a second aspect the present invention relates to a 

process of manufacture of a vinyl acetate based latex composition having a weight average particle size~400 nm, 

including emulsion polymerization of vinyl acetate in the 

presence of polyvinyl alcohol, optionally together with one 

or more additional co-monomer(s), wherein the emulsion 

polymerization is carried out in the presence of 0.0001 wt. 

% to 0.05 wt % of a chain transfer agent, based on total 

monomer weight. The chain transfer agents(s) and the 

amounts used are as defined above. 

The acrylic monomer to be optionally comprised in the 60 

vinyl acetate based polymer latex composition of the invention may for example be selected from the group consisting 

of C1 _s-alkyl acrylates such as ethyl acrylate, butyl acrylate, 

2-ethyl hexyl acrylate or mixtures thereof. The acrylic 

monomer is preferably used in an amount of less than 15% 65 

by weight based on total monomer content, more preferably 

in an amount of 1 to 10% by weight. 

The vinyl acetate based polymer latex composition of the 

invention may be obtained by conventional emulsion polymerization. Conventional batch or semi-batch emulsion 

polymerization procedures may be employed. Mainly for 
US 6,794,466 B2 

9 

safety reasons and in view of the amount of heat to be 

dissipated, the semi-batch procedure is preferred. In case of 

a semi -batch procedure a certain fraction of the reactants 

together with some water, if desired, and some of the 

polyvinyl alcohol solution as well as emulsifier solution, if 5 

used, is initially charged to the reactor. 

The reaction may be stated by feeding an aqueous solution of the initiator or initiator components. Preferred initiation of the emulsion polymerization of the invention is 

carried out by a redox reaction using a redox system of an 10 

oxidant and a reductant in suitable amounts, the amount of 

initiator components to provide complete conversion 

depending on the selected initiator of the redox system. 

Typical oxidants are selected from the group of H20 2, 

organic hydroperoxides such as t-butyl hydroperoxide 

(tBHP), inorganic persulfates such as sodium persulfate, 15 

potassium persulfate and ammonium persulfate. Other 

organic peroxides may be used as well either alone or in 

combination therewith. Typical reductants are the sulfoxylates such as sodium formaldehyde sulfoxylate (SFS), 

sulfites such as sodium sulfite, sodium hydrogen sulfite, 20 

dithionites such as sodium dithionite, and organic reductants 

such as ascorbic acid and its derivatives. Preferred combinations are t-butyl hydroperoxide or hydrogen peroxide and 

sodium formaldehyde sulfoxylate (optionally in the presence of traces of ferro ammonium sulfate), t-BHP or H20 2- 25 

and sodium sulfite, t-BHP or H20 2 and sodium hydrogen 

sulfite, t-BHP or H20 2 and sodium dithionite, t-BHP or 

H20 2 and ascorbic acid, t-BHP or H20 2 and erythorbic acid. 

Thermal initiation by H20 2 or other peroxides may also be 

applied. 30 

Preferably, initiation of the emulsion polymerization is 

carried out by t-BHP or H20 2 and SFS in the presence of 

traces of ferro ammonium sulfate. The initiator is used in 

suitable amounts to provide complete conversion of the 

monomers. In case of the preferred initiation system typi - 35 

cally less than 0.015% by weight t-BHP, based on total 

monomer content, for the course of the polymerization and 

less than 0.15% by weight t-BHP, based on total monomer 

content, for post-polymerization to reduce the residual 

monomer content below 50 ppm, based on the emulsion, is 40 

used. Molar ratios of the SFS are used during the course of 

the polymerization, typically, but are not desired. 

10 

Final latex viscosity at 50% solids by weight will be 

between 1,000 and 40,000 mPas, mainly but not only 

depending on the type and amount of polyvinyl alcohol 

used. Viscosity is measured using a Brookfield viscometer at 

20 rpm at 23° C. 

The vinyl acetate based polymer latex composition of the 

invention thus obtained may be formulated into an adhesive 

by conventional means. In a third aspect the present invention thus relates to an adhesive comprising the above VAc 

based polymer latex composition. Optionally such adhesive 

may comprise suitable additives known to the skilled 

worker. Examples of such additives are plasticizers, antiblocking agents, film forming agents; water-soluble metal 

salts of monobasic acids such as aluminum, chromium 

and/or zirconium salts; free mineral acids such as hydrochloride acid, nitric acid, perchloric acid, phosphoric acid or 

mixtures thereof and antifoam agents (defoamers), biocides, 

and so on. For the use as a water resistant wood glue the 

formulation with metal salts, such as aluminum, chromium 

and/or zirconium salts; free mineral acids, such as hydrochloric acid, phosphoric acid or mixtures thereof is preferred. 

The adhesives of the invention may be characterized as 

follows: 

Paper and packaging adhesives: 

A shear thinning factor SF in the range of 0.1<SF~1.5 

dependent on the desired application. 

A setting speed measured as AZG in seconds of AZG<4 

s. 

A cohesion measured at 70° C. of 24 N/mm2. 

Water resistant wood glues: 

A shear thinning factor SF in the range of 0.1<SF~0.6. 

A setting speed measured as bond strength after 2.5 

minutes gluing time of>1.5 N/mm2. 

A cohesion measured at 80° C. of>6 N/mm2. 

Water resistance of a wood glue of performance group 

D3: D3>2 N/mm2 and water resistance of a wood glue 

of performance group D4: D3~4N/mm2 and D4~4 

N/mm2. 

Properties of latices were measured by the following test 

methods. 

Test Methods 

Latex Particle Size: 

Further on, the remaining fractions of the reactants, the 

PVOH solution as well as the emulsifier solution, if used, 

and extra water, if needed, are fed over a certain period of 45 

time to the reaction vessel. Feeding rates will typically be 

kept constant over the feeding time, but may also vary, if 

desired. Typical reaction times depend on the reaction 

temperature and are typically within the range of 2 hours to 

Final latex particle size distributions were obtained either 

using the COULTER LS230, or using the COULTER N4, 

50 both supplied by Coulter Cooperation, Miami, Florida 

33196. Samples of the final latex were diluted to appropriate 

concentration using pure distilled water. 

8 hours, preferably 4 hours to 6 hours. 

The polymerization reaction of the invention is preferably 

performed at a temperature ranging from 50 to 90° c., 

preferably between 60 and 80° c., during most of the 

reaction time. Care has to be taken that an appropriate 

mixing of the components occurs in the reaction vessel. 55 

Mixing is achieved by conventional means known to the 

skilled worker. Initial reactor charges and procedure can be 

chosen as needed. 

The initiator components will be fed to the reactor during 

all the reaction time, even after the feeding of reactants is 60 

finished until nearly complete conversion is reached. The 

initiator feeding rate may be kept constant or may vary over 

the time. For post-polymerization which is preferably carried out to reduce residual monomer content below 500 ppm 

based on the latex, more concentrated solutions of initiator 65 

components (preferably t- BHP/SFS) are fed to the latex. 

Finally the latex is cooled to ambient temperature. 

Coulter LS230 measurement is based on light diffraction 

combined with some static light scattering and provides a 

particle size distribution. As the larger particles are overestimated by this instrument, the median of the volume distribution function was chosen to characterize an average 

particle size. 

Coulter N4 measurement is based on dynamic light scattering detected at 90 degrees scattering angle. The weight 

average was used to characterize particle size. Each value 

was obtained as an average of 3 measurements. 

Latex Viscosity and Shear Thinning: 

Latex viscosity was measured using Brookfield viscosimeter. Viscosity data were taken for 1, 10 and 20 RPM. The 

latex viscosity is given for 20 RPM (Bf 20) in mPas. To 
US 6,794,466 B2 

11 

characterize the non-Newtonian behavior a shear thinning 

factor SF is calculated from the viscosity at 1 and 10 RPM: 

12 mm to 30 mm i.e. 900 mm2. The coating weight of adhesive 

applied is 100 g each side. The specimens are put together 

and stored for 1 minute without pressure followed by a 

clamping pressure of 0.2 N/mm2 applied for a time of 30 

SF=((Bfl/BflO)-l). A shear thinning factor SF>O indicates 

shear thinning whereas SF <0 stands for shear thickening. All 

measurements were carried out at 23° C. 

Testing of K-value: 

A latex sample was one weighed to obtain 1 gram of 

polymer (not including the PVOH). This sample was diluted 

with 5 ml of pure water. 90 ml of tetra hydrofurane (THF) 

were slowly added under stirring to give a clear polymer 

solution at room temperature. Additional pure water was 

then added to obtain a total amount of 100 ml solution. The 

viscosity of the homogeneous solution was estimated using 

5 minutes. After a storage of 7 days at 23° C./50% reI. 

humidity, the test specimens were stored for 4 hours at a 

temperature of 70° C. in an oven preheated to 70° C. 

Directly following hot storage, the cohesion at 70° C. was 

determined in a tensile shear test, in which the bonded test 

10 specimens were pulled apart using a tensile testing machine 

at a pulling speed of 50 mm/min and were stressed until they 

broke. On fracture, the maximum force F max which occurred 

at that point was determined. The cohesion or thermal 

stability 1: is calculated from 1:=F maxlA, where A is the an Ubbelohde viscosimeter. Calculation of viscosity 

included the Hagenbach correction. The same was carried 

out for a solution representing the solvent including the right 

amount of PVOH and 90 gram of THF. The "Eigenviscosity" k was then calculated based on the Fikentscher Equation. The K-value is then defined by K=103

k. It represents a 

simple viscosimetric average of the polymer molecular 20 

weight. 

15 bonded test area. Final results are mean values from 6 single 

specimens and are given in N/mm2. Performance requirement is to achieve a bond strengt~4 N/mm2. 

Wood Working Adhesive Formulation: 

Base latices, which were polymerized as explained below, 

were formulated to provide the wood working adhesive 25 

formulation. Butyl carbitol acetate was used as a film 

forming agent (2,6 parts per 100 parts of latex). Alumium 

chloride hydrate was then added as a catalyst (3.5 parts of a 

50% solution per 100 parts of emulsion for testing the 

D3-value, or 5 parts of a 50% solution for testing the 30 

D4-values). The components were mixed at ambient temperature. The wood specimens were glued within 1 to 5 days 

after preparation of the formulation. 

Bond Strength in Accordance with DIN EN 204/205: 

Testing of Cohesion at 80° c.: 

As test specimens, pairs of beech wood panels each 5 mm 

thick, 125 mm wide and 325 mm long were bonded to one 

another using the respective adhesive dispersion, under a 

pressure distributed uniformly over the bond area Following 

storage, the bonded panels were divided into test specimens 

each measuring 150 mm in length and 20 mm in width. After 

the test specimens had been prepared they were stored at a 

temperature of 80° C. in an oven preheated to 80° C. 

Directly following hot storage, the thermal stability was 

determined in the tensile shear test on the lines of DIN EN 

Test specimens were produced in accordance with DIN 

EN 205. For this purpose pairs of beech wood panels, each 

5 mm thick, 130 mm wide and 600 mm long, were bonded 

205, in which the bonded test specimens were pulled apart 

using a tensile testing machine at a pulling speed of 50 

mm/min and were stressed until they broke. On fracture, the 

maximum force F max which occurred at that point was 

determined. The cohesion or thermal stability 1: is calculated 

from 1:=F maxi A, where A is the bonded test area Results are 

35 given in N/mm2. Performance requirement is to achieve a 

bond strength~6 N/mm2. 

to one another with the adhesive formulation to be tested Testing the Setting Speed After 2.5 min Setting Time: 

In a manner similar to the procedure for testing the bond 

strength, pairs of oak panels each 5 mm thick, 20 mm wide 

and 150 mm long were bonded using the respective adhesive 

dispersions, with a pressure distributed uniformly over the 

bond area. The bond area was 20 mm*20 mm. Bond strength 

was determined in the tensile shear test after 2.5 minutes, 

where after the bonded test specimens were pulled apart 

using a tensile testing machine at a pulling speed of 50 

mm/min and were stressed until they broke. On fracture, the 

maximum force F max which occurred at that point was 

determined, and was used in turn to determine the bond 

under a pressure distributed uniformly over the bond area 

and were stored in accordance with DIN EN 204. Following 40 

storage, the bonded panels were divided into test specimens 

each measuring 150 mm in length, and these test specimens 

were used to determine the bond strength in the tensile shear 

test. In this test the bonded specimens were pulled apart 

using a tensile testing machine at a pulling rate of 50 45 

mm/min and were stressed until they broke. On fracture, the 

maximum force F max which occurred at that point was 

determined. The bond strength T is calculated in accordance 

with DIN EN 205 from T=FmaxlA, where A is the bonded 

test area Results are given in N/mm2. 50 strength at setting time t by T,,=FmaxlA, where A is the 

bonded test area Results are given in N/mm2. Performance 

requirement is to achieve bond strength> 1.5 N/mm2 after 2.5 

For testing of allocation to performance group D3, the 

specimens, after gluing, were stored under standard climatic 

conditions (23° c., 50% atmospheric humidity) for 7 days 

and then stored in cold water at 20° C. for 4 days. For testing 

of allocation to performance group D4, the specimens, after 55 

gluing, were stored under standard climatic conditions (23° 

c., 50% atmospheric humidity) for 7 days and then stored 

for 6 hours in boiling water, followed by 2 hours in cold 

water at 20° C. Allocation to performance group D3 requires 

to achieve a D3-value~2 N/mm2. Allocation to performance 60 

group D4 requires to achieve a D4-value~4 N/mm2 and a 

D3-value~4 N/mm2. 

Testing of Cohesion at 70° C. 

mm. 

Testing the Setting Speed According to the AZG-Method: 

During the setting of a dispersion based adhesive the 

strength of the bond increases. The setting can be described 

by measuring the change of bond strength with time. In the 

AZG-Method the time is determined necessary that a bonding area of 1 cm2 resists to a load of 2 N applied vertical to 

the bond surface. For formation of the bond 50,u of the 

adhesive are applied to a standard cardboard and a 1 cm2 

piece of cardboard is glued against the adhesive coating. 

After predetermined time the resistance of the bond against 

As test specimens, plywood panels (made from beech the load of 2 N is tested As result the bond resists or it fails. 

wood) each 4 mm thick, 30 mm wide and 135 mm long were 

bonded to one another with an overlapping length of 30 mm 

using the adhesive dispersion tested. The glued area is 30 

65 The whole test is made in an automated device. The test 

procedure is repeated as often as necessary to find the 

shortest time needed to resist to the load of 2 N. This time 
US 6,794,466 B2 

13 14 

is called AZG value. Results are given in seconds. Perfor- Example 3 

mance requirement is to achieve an AZG-value>4 s. 

The following examples are given to further illustrate the 

present invention, but are not intended to limit the same. 

EXAMPLES 

Same as example 1, but 25 PPM of MPA based on mass 

of VAC monomer was added to the initial reactor charge. 

5 The final latex had a Brookfield viscosity of Bf20=6 500 

mnPas. Setting speed was improved as indicated by the drop 

of the AZG-value compared to example 1. 

All examples given below were executed in a 3 I glass 

reactor, equipped with electronic temperature measurement 

and control, reflux condenser, and metering pumps for at 10 

least four different feeds for parallel feeding. Mixing was 

achieved either by using an anchor-type stirrer at 150 rpm, 

constantly, or stirrer speed was increased to 180 rpm during 

the monomer feed period. Few experiments were carried out 

using a cross-beam type stirrer with inclined blades at 400 15 

rpm. 

The ingredients of the recipe were distributed among 

initial reactor charge, feed 1, feed 2, feed 3, feed 4, and feeds 

5 and 6, if applied. The amount of the ingredients was 

chosen to give a final latex of 1800 to 2500 g. The initial 20 

reactor charge was heated and feed 1 (and 2, if used) was 

(were) started at approximately 55° C. to initiate the reaction. Feeds 3 and 4 were started at 65° C. and were metered 

in during 50 to 180 minutes. Reaction temperature was 

maintained between 65 and 80° C. during the addition of 25 

feeds 3 and 4. It was up to 80° C. to 90° C. for the last hour 

where the remaining feed 1 (and 2, if used) were added 

completely, after feeds 3 and 4 were finished 

The free monomer content based on latex after the start of 

feeds 3 and 4 was controlled by appropriate addition rates 30 

for feeds 1, 2, 3, and 4 to be between 2 to 15%. Feed 5 and 

6, if applied, are added after feeds 1 and 2 have been 

completed. The product was cooled to ambient temperature 

under stirring at 100 rpm and application of a vacuum. If 

necessary, a small amount of defoamer was added. 35 

Example 1 (Comparison A) 

Initial reactor charge consisted of 29 parts of a 10% 

PVOH solution and 12.2 parts of water. PVOH used had a 

weight average of molecular mass distribution of Mw=103 40 

000 g/Mol and a number average of Mn=50 400 g/Mol. The 

average degree of hydrolysis was 89%. pH value was 

adjusted to 5.8 by addition of 0.02 parts of 10% NaOH. 13.1 

parts of a VAC monomer were added and finally 0.08 parts 

of a 1 % Ferro ammon sulfate solution were added just before 45 

the start of feed 1 and feed 2. 

Feed 1 consisted of 2.7 parts of a 0.3% hydrogen peroxide 

solution and feed 2 consisted of 2.7 parts of a 1.3% SFS 

solution. Feed 3 consisted of 40 parts of VAC monomer. Post 50 

polymerization was done by feeds 5 and 6 consisting of 0.1 

parts of a 10% tBHP and of 0.1 parts of a 10%0 SFS 

solution, respectively. 

No other feeds were applied. The resulting latex (100 

parts) provided a solid content of 56% for 100% monomer 55 

conversion. Reaction was executed as given above. Final 

latex had a Brookfield viscosity of Bf20=2 600 mPas. 

Example 2 

Example 4 (Comparison B) 

Initial reactor charge consisted of 26 parts of a 10% 

PVOH solution and 16 parts of VAC monomer. PVOH used 

had a weight average of molecular mass distribution of 

Mw=127 800 glMol and a number average of Mn=69 400 

g/Mol. The average degree of hydrolysis was 87%. Reaction 

was started at 60° C. by addition of 0.08 parts of a 20% H2 0 2 

solution. 

Feed 1 consisted of 2.2 parts of a 0.4% H2 0 2 solution. It 

was started 5 min after the initial H2 0 2 addition together 

with feed 3. This feed 1was continuously charged for 480 

min. Feed 3 consisted of 46.3 parts of VAC monomer. It was 

fed for 360 min. Feed 4 consisted of 8.8 parts of pure water 

which was started 60 min after start of feed 3 and which was 

metered in for 240 min. 

Post polymerization was done by feeds 5 and 6 consisting 

of 0.27 parts of a 10% tBHP and of 0.27 parts of a 10% SFS 

solution, respectively. Both feeds were added after feeds 1 

and 2 were completed and after a 1% ferro ammon sulfate 

(FAS) solution of 0.07 parts was added. 

No other feeds were applied. The resulting latex (100 

parts) provided a solid content of 65% for 100% monomer 

conversion. Reaction was executed as given above. The final 

latex had a Brookfield viscosity of Bf20=33 500 mPas. 

Example 5 

Same as example 4, but 200 PPM of croton aldehyde was 

added to the initial reactor charge. The final latex had a 

Brookfield viscosity of 20 500 mPas. 

Example 6 

Same as example 4, but 400 PPM of croton aldehyde was 

added to the initial reactor charge. The final latex had a 

viscosity of Bf20=20 300 mPas. 

Example 7 

Same as example 4, but an effective amount of 360 PPM 

of propionic aldehyde was added to the initial reactor 

charge. The final latex after dilution to 61.5% had a viscosity 

of 20 200 mPas. 

Example 8 (Comparison C) 

Initial reactor charge consisted of 37.9 parts of a 10% 

PVOH solution together with 6.7 parts of water. The PVOH 

used had a weight average of molecular mass distribution of 

Mw=149 200 glMol and a number average of Mn=94 600 

g/Mol. The average degree of hydrolysis was 91 %. pH of the 

aqueous solution was adjusted to 5.8 by addition of 0.05 

parts of a 10% NaOH solution Initial VAC monomer charge 

was 12.3 parts. Additionally 0.05 parts of a 1 % FAS solution 

Same as example 1, but 12.5 parts per million of 

3-mercapto propionic acid (MPA) based on mass of VAC 

monomer was added to the initial reactor charge. The final 

latex had a Brookfield viscosity of Bf20=5 700 mPas. Shear 

thinning was improved, as indicated by the larger SF-value 

compared to example 1. Setting speed was improved as 

indicated by the drop of the AZG-value compared to 

example 1. 

60 were added before starting the feeds 1 and 2. 

Feed 1 consisted of 0.82 parts of a 0.25% TBHP solution, 

metered in for 200 min. Feed 2 consisted of 0.82 parts of a 

0.38% SFS solution which was fed parallel to feed 1. Feed 

3 consisted of 36.6 parts of VAC monomer which was fed in 

65 for 160 min. Feed 4 consisted of 0.3 parts of N-methylol 

acryl amide together with 4.3 parts of water. This was fed 

parallel to feed 3. 
US 6,794,466 B2 

15 

Post polymerization was done by feeds 5 and 6, consisting 

of 0.1 parts of a 10% tBHP solution and 0.1 parts of a 10% 

SFS solution, respectively. The resulting latex (100 parts) 

provided a solid content of 53% for 100% monomer conversion Reaction was executed as given above. The final 5 

latex, diluted to 50% solids, had a Brookfield viscosity of 

Bf20=5 920 mPas. 

Example 9 

Same as example 8, but 25 PPM of MPA was fed within 10 

feed 4 during the reaction. The final latex, diluted to 50%, 

had a Brookfield viscosity Bf20=5 730 mPas. 

Example 10 

Same as example 8, but 45 PPM of MPA were fed within 15 

feed 4 during the reaction. The final latex, diluted to 50%, 

had a Brookfield viscosity Bf20=6 090 mnPas. 

Example 11 

Same as example 8, but 90 PPM of MPA were fed within 20 

feed 4 during the reaction. The final latex, diluted to 50%, 

had a Brookfield viscosity Bf20=6 670 mnPas. 

Example 12 (Comparison D) 

Same as example 8, but 180 PPM of MPA were fed within 25 

feed 4 during the reaction. The final latex, diluted to 50%, 

had a Brookfield viscosity Bf20= 7 530 mPas. 

Example 13 (Comparison E) 

30 Same as example 8, but 360 PPM of MPA were fed within 

feed 4 during the reaction. The final latex, diluted to 50%, 

had a Brookfield viscosity Bf20=6 870 mPas. 

16 

PVOH was used as in example 16. pH of the aqueous 

solution was adjusted to 5.8 by addition of 0.01 parts of a 

10% NaOH solution. Initial VAC monomer charge was 12 

parts. Additionally 0.05 parts of a 1% FAS solution were 

added just before start of feeds 1 and 2. 

Feed 1 consisted of 2 parts of a 0.25% tBHP solution, 

metered in for 200 min. Feed 2 consisted of 2 parts of a 

0.38% SFS solution which was fed parallel to feed 1. Feed 

3 consisted of 35.83 parts of VAC monomer and was 

metered in for 160 min. Feed 4 consisted of 0.9 parts of 

N-methylol acryl amide together with 3 parts of water. This 

was fed parallel to feed 3. 

Post polymerization was done by feeds 5 and 6, consisting 

of 0.1 parts of a 10% tBHP solution and 0.1 parts of a 10% 

SFS solution, respectively. The resulting latex (100 parts) 

provided a solid content of 52.5% for 100% monomer 

conversion. Reaction was executed as given above. The final 

latex, diluted to 50% solids, had a Brookfield viscosity of 

Bf20=16 730 mPas. Rheological behavior indicated strong 

shear thickening with a negative shear thinning factor SF. 

Example 18 

Same as example 17, but 25 PPM of MPA was fed within 

feed 4 during the reaction. Final latex, diluted to 50%, had 

a Brookfield viscosity Bf20=10 060 mPas. The shear thickening behavior of example 17 was converted to shear 

thinning behavior. 

Example 19 

Example 14 (Comparison F) 

Same as example 8, but 720 PPM of MPA were fed within 

feed 4 during the reaction. The final latex, diluted to 50%, 

had a Brookfield viscosity Bf20=5 400 mPas. 

Same as example 18, but monomer feed 3 comprised by 

35 95% of VAC and 5% of VeoVa9 monomer (ast supplied by 

Shell). The final latex, diluted to 50% solids, had a Brookfield viscosity of Bf20=9 050 mPas. 

Example 15 (Comparison G) Example 20 (Comparison I) 

40 

Same as example 8, but instead of a anchor type stirrer a 

cross-beam type stirrer with inclined blades was used at 400 

RPM. The final latex, diluted to 50% had a Brookfield 

viscosity Bf20=9 800 mPas. The rheological behavior 

clearly indicated shear thickening with a negative shear 45 

thinning factor SF. 

Same as example 17, but monomer feed 3 comprised by 

85% of VAC and 15% of Yeo Va9 monomer. The final latex, 

diluted to 50% solids, had a Brookfield viscosity of Bf20=10 

800 mpas. 

Example 21 

Example 16 

Same as example 15, but 25 PPM of MPA was fed within 

feed 4 during the reaction. The final latex, diluted to 50%, 

had a Brookfield viscosity Bf20=8 420 mPas. Shear thickening behavior of example 15 was converted to shear 

thinning behavior. 

Example 17 (Comparison H) 

Initial reactor charge consisted of 37.1 parts of a 10% 

PVOH solution together with 6.9 parts of water. The same 

Same as example 20, but 25 PPM of MPA was fed within 

feed 4 during the reaction. The final latex, diluted to 50% 

50 solids, had a Brookfield viscosity of Bf20=8 660 mpas. 

Example 22 

Same as example 21, but NMA content in feed 3 was 

55 raised from 0.9 parts to 1.05 parts. The final latex, diluted to 

50% solids, had a Brookfield viscosity of Bf20=8 000 

mnPas. 
US 6,794,466 B2 

17 18 

TABLE 1 

Latex and Adhesive Performance 

final setting s12eed cohesion 

particle paper wood wood wood 

erA size K s.c. Bf20 AZG 2.5 min 70° C. 80° C. 

Example PPM nm Value % mPas SF N/mm2 N/mm2 N/mm2 

lA 0 1187 '

) 115 56 2600 0.65 

2 12.5 A) 932') 134 56 5700 1.13 

3 25.0 A) 907 '

) 132 56 6500 1.19 

4B 0 1551 2) 112 65 33500 0.80 

5 200 B) 1357 2) 113 65 20500 0.92 

400 B) 11122) 107 65 20300 1.02 

7 360 C) 1283 2) 96 61.5 20200 lAS 

8C 0 935 '

) 136 50 5920 0.25 

9 25 A) 822') 142 50 5730 0.30 

10 45 A) 777 '

) 135 50 6090 0045 

11 90 A) 760 '

) 117 50 6670 0.54 

120 180 A) 743 '

) 102 50 7530 0.64 

BE 360 A) 1050 '

) 91 50 6870 0.39 

14 F 720 A) 1045 '

) 76 50 5400 0040 

15 G 0 1440 '

) 134 50 9800 -0.16 

16 25 D) 1020 '

) 145 50 8420 0.15 

17H 0 1950 2) 136 50 16730 -0.24 

18 25 A 1050 2) 131 50 10060 0.21 

19 25 A) 1236 2) 123 50 9050 0.15 

20 I 0 1176 2) 119 50 10800 0.08 

21 25 A) 1226 2) 124 50 8660 0.21 

22 25 A) 1170 2) 126 50 8000 0.31 

A)CTA 3-mercato propionic acid 

B)erA croton aldehyde 

C)erA propion aldehyde 

D)CTA 2-mercapto propionic acid 

'>particle size median X 3•

50 from COULTER LS 230 analysis 

2>particle size weight average from COULTER N4 analysis 

Example 

9 

10 

11 

16 

18 

19 

21 

22 

TABLE 2 

Wood Glue Performance 

03-value 

N/mm2 

2.8 

3.0 

2.9 

2.3 

304 

3.9 

5.3 

5.5 

04-value 

N/mm2 

1.8 

3.1 

3.0 

4.1 

4.0 

6.0 

3.8 

3.0 

5.7 

2.7 

3.7 

3.5 

1.5 

1.9 

2.0 

2.0 

2.1 

2.3 

2.0 

1.5 

1.8 

1.1 

2.0 

204 

1.7 

2.8 

2.2 

4.6 

404 

4.3 

4.5 

4.5 

4.2 

4.0 

7.2 

7.0 

7.2 

6.5 

5.5 

5.1 

5.2 

7.2 

7.3 

704 

7.5 

7.2 

6.8 

7.1 

7.1 

35 (SF<O) to a shear thinning one (SF>O) within the desired 

range of SF. At the same time the setting speed is improved 

without impairing cohesion. 

Additionally, the results of the comparative Examples 

12D, 13E, 14F demonstrate, that use of a CTA above the 

40 limits of this invention in accordance with the prior art will 

result in a much higher decrease of the average molecular 

weight, expressed as the K-value, and will thereby contribute to an unacceptable loss or reduction of cohesion. 

Examples 21 and 22 represent VAC co-polymers suitable 

45 as a base of high performance boiling water resistant D4 

wood glues. Comparing Examples 21 and 22 with 20L both 

the setting speed and the shear thinning are improved by use 

trace amounts of aCTA. 

We claim: 

In Table 1 the results of the 13 examples, and 9 compara- 50 

tive examples are summarized. Table 2 summarizes results 

obtained for the water resistance of the bond when base 

emulsions obtained in the framework of this invention were 

formulated as wood glues. 

1. Vinyl acetate based polymer latex composition 

obtained by emulsion polymerization of: 

(a) polyvinyl alcohol, 

(c) a monomer mixture comprising vinyl acetate, and (d) 

optionally one or more additional co-monomer(s), 

Examples 2, 3, 5, 6, and 7 represent VAC homopolymer 

latices of this invention prepared in the presence of PVOH. 

The comparison with Example 1 reveals that the use of trace 

amounts of CTA results in the following: the setting speed 

measured as AZG is considerably increased, the shear thinning may be adjusted within the required range, cohesion 

stays within its desired range and K-value is slightly 

increased or remains about unchanged. 

Examples 9, 10, 11, 16, 18, 19, 21, and 22 represent VAC 

co-polymers suitable as base of high performance water 

resistant D3 wood glues. Comparing Example 16 with 15G, 

and 18 with 17H it is obvious that the use of trace amounts 

of a CTA may even convert a shear thickening behavior 

55 in presence of (c) 0.0001-0.05 wt. % of a chain transfer 

agent, based on total monomer weight, said vinyl acetate 

based polymer latex composition having a weight average 

particle size ~400 nm and a higher shear thinning factor 

than the vinyl acetate based polymer latex composition (a), 

60 (b) and (d) obtained in the absence of the chain transfer 

agent (c). 

2. Composition according to claim 1, wherein emulsion 

polymerization is carried out in presence of 0.001 to 0.05 wt. 

% of a chain transfer agent selected from the group consist65 ing of aldehydes and chain transfer agents having a similar 

chain transfer constant with regard to vinyl acetate as the 

monomer. 
US 6,794,466 B2 

19 

3. Composition according to claim 1, wherein emulsion 

polymerization is carried out in presence of 0.0001 to 0.01 

wt. % of a chain transfer agent selected from the group 

consisting of thiols, mercapto acids, and chain transfer 

agents having a similar chain transfer constant with regard 

to vinyl acetate as the monomer. 

4. Composition according to claim 1, having a shear 

thinning factor of about 1,2 to 3,5 times the shear thinning 

factor of a latex composition obtained in absence of the 

chain transfer agent or wherein the shear thinning factor is 

shifted from negative values to positive values. 

5. Composition according to claim 1, wherein the latex 

weight average particle size is about 60 to 95% the weight 

average particle size of a latex composition obtained in the 

absence of the chain transfer agent. 

6. Composition according to claim 1, wherein the chain 

transfer agent is selected from the group consisting of 

C2 _

s-aldehydes, C2 _s-thiols, C2 _s-mercaptoacids, and mixtures thereof. 

7. Composition according to claim 2, wherein the chain 

transfer agent is selected from the group consisting of croton 

aldehyde, propionic aldehyde, and mixtures thereof. 

20 

14. Composition according to claim 13, wherein the 

post-crosslinking monomer is N-methylol acrylamide. 

15. Composition according to claim 8, wherein the vinyl 

acetate based polymer latex composition is a copolymer of 

5 vinyl acetate/N-methylol acrylamide, optionally further 

including versa tic acid vinyl ester having 9 to 10 carbon 

atoms from the carbonic acid group. 

16. Process of manufacture of a vinyl acetate based 

polymer latex composition having a weight average particle 

10 size ~400 nm, including emulsion polymerization of vinyl 

acetate in the presence of polyvinyl alcohol, optionally 

together with one or more additional co-monomer(s), 

wherein the emulsion polymerization is carried out in the 

presence of 0.0001 wt. % to 0.05 wt. % chain transfer agent, 

15 based on total monomer weight. 

17. Process according to claim 16, wherein emulsion 

polymerization is carried out in presence of 0.001 to 0.05 wt. 

% of a chain transfer agent selected from the group consisting of aldehydes and chain transfer agents having a similar 

20 chain transfer constant with regard to vinyl acetate as the 

monomer. 

8. Composition according to claim 3, wherein the chain 

transfer agent is selected from the group consisting of 

2-mercapto propionic acid, 3-mercapto propionic acid, and 25 

mixtures thereof. 

18. Process according to claim 16, wherein emulsion 

polymerization is carried out in presence of 0.0001 to 0.01 

wt. % of a chain transfer agent selected from the group 

consisting of thiols, mercapto acids, and chain transfer 

agents having a similar chain tansfer constant with regard to 

9. Composition vinyl acetate as the monomer. according to claim 1, wherein the amount 

of vinyl acetate is in the range of 100 wt. % to 60.00 wt. %, 

based on total monomer weight. 

10. Composition according to claim 1, wherein the polyvinyl alcohol has a degree of hydrolysis from 60 to 99 

mole-% and is present in an amount of 3 wt. % to 12 wt. %, 

based on total monomer weight. 

19. Process according to claim 17, wherein the chain 

transfer agent is selected from the group consisting of croton 

30 aldehyde, propionic aldehyde or mixtures thereof. 

11. Composition according to claim 1, wherein the vinyl 

acetate based polymer latex composition further comprises 35 

one or more co-monomers selected from the group consisting of one or more vinyl ester(s), other than vinyl acetate, 

one or more post-crosslinking monomer(s), one or more 

ethylenically unsaturated acid(s) or anhydride(s) thereof, 

one or more acrylic monomer(s), and mixtures thereof. 40 

12. Composition according to claim 11, wherein the one 

or more vinyl ester(s) are selected from the group consisting 

20. Process according to claim 18, wherein the chain 

transfer agent is selected from the group consisting of 

2-mercapto propionic acid, 3-mercapto propionic acid or 

mixtures thereof. 

21. Process according to claim 16, wherein the vinyl 

acetate based polymer is a co-polymer of vinyl acetate/Nmethylol acrylamide, optionally fierier including versatic 

acid vinyl ester having 9 or 10 carbon atoms from the 

carbonic acid group, and the chain transfer agent is mercapto 

propionic acid. 

22. Adhesive, comprising the vinyl acetate based polymer 

latex composition according to claim 1. of vinyl propionate, vinyl pivalate, vinyl 2-ethyl hexanoate, 

diisopropyl maleate, diisopropyl fumarate, versa tic acid 

vinyl esters having 9 to 10 carbon atoms from the carbonic 

acid group, and mixtures thereof, the one or more additional 

vinyl ester(s) being present in an amount of up to 40 wt %, 

based on total monomer weight. 

23. Adhesive, comprising the vinyl acetate based polymer 

45 latex composition according to claim 15. 

13. Composition according to claim 11, wherein the one 

or more post-crosslinking monomer(s) are selected from 

N-alkoyl derivatives of an amide of a a,~-ethylenically 

unsaturated carboxylic acid. 

24. Adhesive according to claim 22, for use in paper and 

packaging, comprising a vinyl acetate homopolymer latex 

composition. 

25. Adhesive according to claim 23 for use as a wood 

50 glue. 

* * * * *